High voltage photovoltaics integrated with light emitting diode

ABSTRACT

An electrical device that includes a material stack present on a supporting substrate. An LED is present in a first end of the material stack having a first set of bandgap materials. A photovoltaic device is present in a second end of the material stack having a second set of bandgap materials. The first end of the material stack being a light receiving end, wherein a widest bandgap material for the first set of bandgap material is greater than a highest bandgap material for the second set of bandgap materials.

BACKGROUND Technical Field

The present invention generally relates to photovoltaic devices, andmore particularly to photovoltaic devices used to power light emittingdiodes.

Description of the Related Art

A photovoltaic device is a device that converts the energy of incidentphotons to electromotive force (e.m.f.). Typical photovoltaic devicesinclude solar cells, which are configured to convert the energy in theelectromagnetic radiation from the sun to electric energy. Alight-emitting diode (LED) is a two-lead semiconductor light source. Itis a p-n junction diode, which emits light when activated. When asuitable voltage is applied to the leads to the LED, electrons are ableto recombine with electron holes within the device, releasing energy inthe form of photons. This effect is called electroluminescence, and thecolor of the light (corresponding to the energy of the photon) isdetermined by the energy band gap of the semiconductor.

SUMMARY

In accordance with one embodiment, an electrical device is describedherein that includes a photovoltaic structure in combination with alight emitting diode (LED) structure, wherein the photovoltaic structureprovides the power to the LED. In one embodiment, a material stack isprovided that includes an LED device at a first end of the materialstack and a photovoltaic device at a second end of the material stack.The LED device has a first set of bandgap materials, and thephotovoltaic device has a second set of bandgap materials, the first endof the material stack being a light receiving end, wherein a widerbandgap material for the first set of bandgap material is greater than ahighest bandgap material for the second set of bandgap materials.

In another embodiment, an electrical device is provided that includes amaterial stack is having a photovoltaic device at a first end of thematerial stack and an LED structure at a second end of the materialstack. The LED device has a first set of bandgap materials, and thephotovoltaic device has a second set of bandgap materials, the first endof the material stack being a light receiving end, wherein a widerbandgap material for the second set of bandgap material is greater thana highest bandgap material for the first set of bandgap materials.

In another aspect, a method of forming an electrical device is describedherein that in one embodiment includes providing a material stackincluding an LED portion and a photovoltaic portion. The LED portion iscomprised of semiconductor material layers having a first set ofbandgaps. The photovoltaic portion is comprised of semiconductormaterial layers having a second set of bandgaps. The LED portion of thematerial stack is at a first end of the material stack and thephotovoltaic portion is present at a second end of the material stack,wherein the device having the first or second set of bandgaps having thewider band gap is positioned at the light end receiving end of thematerial stack. In one embodiment, the method of forming the electricaldevice may include growing a first junction on a supporting substrate;and forming a second junction on the first junction by molecular beamepitaxial growth. Contact may then be formed to the first junction andthe second junction, wherein a first device of the first and the secondjunction is a photovoltaic device, and a second device of the first andthe second junction is a light emitting diode. The semiconductormaterial layers in the LED or the photovoltaic device that is at a lightreceiving end of the electrical device have a wider band gap than theLED or the photovoltaic device that is not at the light receiving end ofthe electrical device.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a side cross-sectional view depicting one embodiment of a highvoltage photovoltaic cell including gallium nitride (GaN) that isintegrated with a light emitting diode (LED), in which the LED device ispositioned between the supporting substrate and the photovoltaic device.

FIG. 2 is a side cross-sectional view depicting one embodiment of a highvoltage photovoltaic cell including gallium nitride (GaN) that isintegrated with a light emitting diode (LED), in which the photovoltaicdevice is positioned between the supporting substrate and the LED.

FIG. 3 is a side cross-sectional view depicting one embodiment of a highvoltage photovoltaic cell including aluminum gallium nitride (AlGaN)that is integrated with a light emitting diode (LED), in which the LEDdevice is positioned between the supporting substrate and thephotovoltaic device.

FIG. 4 is a side cross-sectional view depicting one embodiment of a highvoltage photovoltaic cell including aluminum gallium nitride (GaN) thatis integrated with a light emitting diode (LED), in which thephotovoltaic device is positioned between the supporting substrate andthe LED.

FIG. 5 is a flow chart describing one embodiment of a method for forminghigh voltage photovoltaics that are integrated with LEDs, in which themethod includes a low hydrogen deposition process.

FIG. 6 is a flow chart of another embodiment of a method for forminghigh voltage photovoltaics that are integrated with LEDs.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the invention, as it is oriented inthe drawing figures. The terms “overlying”, “atop”, “positioned on” or“positioned atop” means that a first element, such as a first structure,is present on a second element, such as a second structure, whereinintervening elements, such as an interface structure, e.g. interfacelayer, may be present between the first element and the second element.The term “direct contact” means that a first element, such as a firststructure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

In one embodiment, the present disclosure provides photovoltaic cells,i.e., photovoltaic devices, needed for internet of things (IOT)applications that also include light emitting diodes (LEDs). As usedherein, a “photovoltaic device” is a device, such as a solar cell, thatproduces free electrons and/or vacancies, i.e., holes, when exposed toradiation, such as light, and results in the production of an electriccurrent. In some embodiments, a multi-junction photovoltaic deviceincludes a multiple junctions of a semiconductor layer of a p-typeconductivity that shares an interface with a semiconductor layer of ann-type conductivity, in which the interface provides an electricaljunction. As used herein, the term “LED” denotes a semiconductormaterial containing structure that emits light when an electricalcurrent is passed through it. In some embodiments, the light-emittingdiode (LED) is a two-lead semiconductor light source, which can resemblea pn-junction diode. In this example, when a voltage is applied to theleads to the pn-junction type diode, electrons are able to recombinewith electron holes within the device, releasing energy in the form ofphotons. This effect is called electroluminescence, and the color of thelight (corresponding to the energy of the photon) is determined by theenergy band gap of the semiconductor.

Physically small, i.e., devices having a small footprint, having highvoltage requirements are needed. The length and width dimensions of themonolithically formed devices of high voltage photovoltaics integratedwith LEDS that are described herein may be no greater than 150 microns,e.g, may be equal to 100 microns or less.

In some embodiments, the voltage requirements can be met by amulti-junction photovoltaic cells, as depicted in FIG. 1. The voltagerequirements for a photovoltaic device of this type may be between 2volts and 3 volts to drive light emitting diodes (LEDs) forcommunication applications. The voltage requirements to write and readmemory cells may range from 2 volts to 3.5 volts. In batteryapplications, the photovoltaic devices may need to provide 3.5 volts tocharge a battery.

In some embodiments, an integrated LED is needed to send signal tooutside the device. Monolithically integrated LEDs with photovoltaicdevices can reduce size of an electrical device that includes an LEDthat is separate from a photovoltaic device or other power source. Insome embodiments, the structures and methods disclosed herein provide ahigh voltage photovoltaic device that is integrated with an LED that maybe used for energy harvesting and communication, in which the integrateddevice is formed using semiconductor growth processes, which may includegrowth processes using low hydrogen content precursors.

The photovoltaic device 100 a depicted in FIG. 1 may be composed of amaterial stack 50 including a LED device 15 and a photovoltaic device 10that is present on a supporting substrate 5. The LED device 15 may bepresent at a first end of the material stack having a first set ofbandgap materials 12, 13, 14; and the photovoltaic device at a secondend of the material stack having a second set of bandgap materials 8, 9.A band gap, also called an energy gap or bandgap, is an energy range ina solid where no electron states can exist. In graphs of the electronicband structure of solids, the band gap generally refers to the energydifference (in electron volts) between the top of the valence band andthe bottom of the conduction band in insulators and semiconductors. Itis the energy to promote a valence electron bound to an atom to become aconduction electron, which is free to move within the crystal latticeand serve as a charge carrier to conduct electric current.

In some embodiments, because the LED device 15 and the photovoltaicdevice 10 are included within the same material stack 50, the devices10, 15 are monolithographically integrated onto the same substrate 5. Insome embodiments, the LED device 15 and the photovoltaic device 10 arein direct contact, i.e., there is no material layer present between andseparating the LED device 15 from the photovoltaic device 10. In each ofthe combinations of electrical devices described herein, the materiallayers for the photovoltaic device 10 are selected to produce enoughpower to cause the LED 15 to emit light. In the embodiments in which thephotovoltaic device 10 is present atop the LED 15, and the LED 15 emitslight in the direction through the photovoltaic device 10, the bandgapmaterials of the photovoltaic device 10 and the LED device 15 areselected so that the wavelengths of light emitted by the LED 15 are notabsorbed by the photovoltaic device 10.

In each of the electrical devices described herein, including aphotovoltaic device 10 and a LED device 15 integrated within the samematerial stack 50 of semiconductor materials, the bandgaps of thematerials are selected so that the device composed of the wider bandgapmaterials, e.g., LED device 15 or photovoltaic device 10, is present atthe top of the device, i.e., the light receiving end of the device; andthat the device composed of the narrower bandgap materials, e.g., LEDdevice 15 or the photovoltaic device 10, is present at the base of thedevice, i.e., the end of the device that is furthest from the lightsource.

Referring to FIG. 1, the photovoltaic device 10 is positioned at the endof the material stack 50 at which at the light (identified by referencenumber 3) first enters the device, which is the light receiving end ofthe device. In the embodiment depicted in FIG. 1, the photovoltaicdevice 10 is present at the light receiving end of the material stack 50and is composed of a p-type conductivity gallium and nitride containinglayer 8, i.e., p-type gallium nitride (GaN), that forms a junction bydirect contact to an n-type conductivity gallium and nitride containinglayer 9, i.e., n-type gallium nitride (GaN). The band gap for galliumnitride (GaN) is on the order of 3.4 eV. The photovoltaic device 10 thatis depicted in FIG. 1 when receiving a light wavelength ranging from 250nm to 350 nm can provide a voltage that is greater than 2.0 eV. In yetother examples, the voltage produced by the photovoltaic device isgreater than 2.25 eV. For example, the photovoltaic device 10 thatincludes the junction of the n-type gallium nitride (GaN) layer and thep-type gallium nitride (GaN) layer that is depicted in FIG. 1 mayproduce a voltage of 2.5 V or greater. It is noted that the aboveexamples are provided for illustrative purposes only, and are notintended to limit the present disclosure. In other examples, the voltageproduced by the photovoltaic device 10 composed of the n-type and p-typeconductivity gallium nitride (GaN) layers depicted in FIG. 1 may beequal to 2.0 V, 2.25 V, 2.5 V, 2.75 V, 3.0 V, 3.25 V, and 3.5V, as wellas any value between the aforementioned examples, and any range ofvoltages having a lower limit provided by one of the aforementionedexample voltages, and an upper limit provided by one of theaforementioned example voltages.

Each of the p-type conductivity gallium and nitride containing layer 8,e.g., p-type gallium nitride (GaN), and the n-type conductivity galliumand nitride containing layer 9, e.g., n-type gallium nitride (GaN) canhave a thickness ranging from 100 nm to 2000 nm.

As used herein, “p-type” refers to the addition of impurities to anintrinsic semiconductor that creates deficiencies of valence electrons.As used herein, “n-type” refers to the addition of impurities thatcontributes free electrons to an intrinsic semiconductor. In a typeIII-V semiconductor material, the effect of the dopant atom, i.e.,whether it is a p-type or n-type dopant, depends upon the site occupiedby the dopant atom on the lattice of the base material. In a III-Vsemiconductor material, atoms from group II act as acceptors, i.e.,p-type, when occupying the site of a group III atom, while atoms ingroup VI act as donors, i.e., n-type, when they replace atoms from groupV. Dopant atoms from group IV, such a silicon (Si), have the propertythat they can act as acceptors or donor depending on whether they occupythe site of group III or group V atoms respectively. Such impurities areknown as amphoteric impurities. The dopant that provides the n-typeconductivity for the n-type conductivity gallium and nitride containinglayer 9 may be present in a concentration ranging from 10¹⁷ atoms/cm³ to10²⁰ atoms/cm³. The dopant that provides the p-type conductivity of thep-type conductivity gallium and nitride containing layer 8 may bepresent in a concentration ranging from 10¹⁷ atoms/cm³ to 10²⁰atoms/cm³.

In some embodiments, the light to power the photovoltaic device 10 ofthe p-type conductivity gallium and nitride containing layer 8 and then-type conductivity gallium and nitride containing layer 9 may rangefrom 250 nm to 350 nm. In another embodiment, the light to power thephotovoltaic device 10 having the junction of the p-type conductivitygallium and nitride containing layer 8 and the n-type conductivitygallium and nitride containing layer 9 is equal to approximately 300 nm.

The p-type conductivity gallium and nitride containing layer 8 and then-type conductivity gallium and nitride containing layer 9 of thephotovoltaic device 10 are a first set of bandgap materials, while thematerial layers in the LED device 15 are a second set of bandgapmaterials. The minimum bandgap for the first set of bandgap materials,i.e., the minimum bandgap materials for the material layers in thephotovoltaic device 10, is wider, i.e., greater, than the minimumbandgap for the second set of bandgap materials, i.e., the minimumbandgap materials for the material layers in the LED device 15.

In the embodiment that is depicted in FIG. 1, the end of the materialstack 50 at which the light emitting diode (LED) 15 is positioned isfurther from the light receiving end of the device than the end of thematerial stack 50 at which the photovoltaic device 10 is positioned. Inthe embodiment that is depicted in FIG. 1, the LED 15 is positionedbetween the supporting substrate 4 and the photovoltaic device 10. Thesupporting substrate 4 can be composed of n-type gallium nitride. Then-type gallium nitride containing photovoltaic junction layer 9 can bein direct contact with the LED device 15. The LED device 15 may includea p-type gallium nitride containing layer 12 that is in direct contactwith a first end of a multi quantum well 13, and an n-type galliumnitride containing layer 14 that is direct contact with an opposingsecond end of the multi quantum well 13. The p-type gallium nitridecontaining layer 12 of the LED device 15 may be referred to as a firstcladding layer, and the n-type gallium nitride containing layer 14 maybe referred to as a second cladding layer.

In some embodiments, the first and second cladding layers, i.e., thep-type gallium nitride containing layer 12 and the n-type galliumnitride containing layer 14 of the LED 15, function to pump chargecarriers, i.e., electron and hole charge carriers, into the intrinsicactive area provided by the quantum well 13 of the LED 15. The dopantthat provides the conductivity type, i.e., whether the gallium nitridecontaining layer 12, 14 is n-type or p-type, may be present in aconcentration ranging from 10¹⁷ atoms/cm³ to 10²⁰ atoms/cm³. In someexamples, the p-type gallium nitride containing layer 12 and the n-typegallium nitride containing layer 14 may have a thickness ranging from100 nm to 2000 nm. It is noted that the above compositions andthicknesses are provided for illustrative purposes only, and are notintended to limit the present disclosure.

The active region of the LED device 15 is in the intrinsic (I) region,which is within the quantum well 13. By “intrinsic” it is meant that theregion is not doped with an extrinsic dopant, e.g., n-type or p-typedopant, such as the dopants used to dope the first and second claddinglayers, i.e., the p-type gallium nitride containing layer 12 and then-type gallium nitride containing layer 14. The active region in thequantum well structure is formed by alternating layers of relatively lowbandgap material and layers of relatively high bandgap material. As usedherein, a “low bandgap” is a bandgap ranges from 0.5 eV to 3.0 eV, and a“high bandgap” ranges from 3.1 eV to 3.5 eV. The former layers aretermed “well layers” and the latter layers are termed “barrier layers.”For example, for the quantum well 13, e.g., multi-quantum well, thematerial layers providing the relatively high bandgap material may begallium nitride (GaN), and the material layers having the relatively lowbandgap material may be indium gallium nitride (InGaN). Indium galliumnitride (InGaN) has a band gap of approximately 2.7 eV, while galliumnitride (GaN) has a band gap of approximately 3.4 eV. The band gap ofapproximately 2.7 eV for the indium gallium nitride (InGaN) portion ofthe multi-quantum well 13 can provide the minimum value for the secondset of bandgap materials for the LED 15 that is less than the minimumvalue, i.e., is narrower than, the minimum bandgap of the wider bandgapmaterials for the overlying first set of bandgap materials for thematerial layers of the photovoltaic device 10.

To provide the stacked structure of quantum wells, the thickness of eachlayer of semiconductor material within the quantum well may be nogreater than 50 nm. For example, the thickness for each layer of theIII-V compound semiconductor material, e.g., high band gap GaN and/orlow band gap InGaN, within the quantum well 13 may range from 5 nm to 10nm. In some embodiments, the stacked structure of quantum wells may becomposed of 1 to 100 layers of semiconductor material, such as III-Vcompound semiconductor materials, e.g., the high band gap GaN and/or lowband gap InGaN. In yet another embodiment, the stacked structure ofquantum wells 13 may be composed of 1 to 5 layers of semiconductormaterial layers.

The active region consisting of one or more indium gallium nitride(InGaN) including quantum wells 13 sandwiched between thicker layers ofgallium nitride (GaN), i.e., cladding layers 12, 14, may provide an LED15 that provides for blue light emission. For example, the LED device 15that is depicted in FIG. 1 may emit light having a wavelength ofapproximately 450 nm. The wavelength of light being emitted by the LED15 is not absorbed by the photovoltaic device 10 that the light from theLED 15 is being passed through. In some embodiments, by varying therelative In/Ga fraction in the InGaN including quantum wells 13, thelight emission can in theory be varied from violet to amber. It is notedthat the wavelength of approximately 450 nm is only one example of alight wavelength that may be emitted by the LED 15. In some otherexamples, the light wavelength that may be emitted by an LED 15 similarto that depicted in FIG. 1 may be equal to 400 nm, 410 nm, 420 nm, 430nm, 440 nm, 450 nm, 460 nm, 470 nm, 480 nm, 490 nm and 500 nm, as wellas any range of values having a lower limit selected from theaforementioned examples, and an upper limit selected from theaforementioned examples, e.g., a range extending from 430 nm to 470 nm.As noted above, the LED 15 may be powered by the voltage produced by thephotovoltaic device 10, e.g., a voltage of greater than 2.0 V. In someembodiments, the LED 15 may be powered by the voltage produced by thephotovoltaic device 10, e.g., a voltage greater than 2.5 V.

The LED 15 may be positioned on semiconductor substrate 5. In someembodiments, the semiconductor substrate 5 is composed of an n-typeIII-V semiconductor material, such as gallium nitride, e.g., n-type GaN.

The high voltage GaN photovoltaic cells that are integrated with InGaNLED structures that are depicted in FIG. 1 may also include a glasssubstrate 4 on the light receiving end of the device.

Contacts 21, 22, 31, 32 may be formed to each of the photovoltaic device10 and the LED 15. For example, a first LED device contact 21 may be inelectrical communication with the n-type gallium nitride (GaN) layerthat provides a cladding layer of the LED 15 on a first side of thequantum well 13 of the device, and a second LED device contact 22 may bein electrical communication with the p-type gallium nitride (GaN) layeron the opposing side of the quantum well 13 of the device. A firstphotovoltaic device contact 31 may be formed on the n-type galliumnitride (GaN) layer 9 of the photovoltaic device 10; and a secondphotovoltaic device contact 32 may be formed on the p-type galliumnitride layer (GaN) layer of the photovoltaic device 10. Each of thecontacts 21, 22, 31, 32 may be composed of an electrically conductivematerial, such as a metal, e.g., copper, tungsten, aluminum, tantalum,silver, platinum, gold and combinations and alloys thereof.

FIG. 2 depicts another embodiment of an electrical device 100 bincluding a high voltage photovoltaic device 10 of gallium nitride (GaN)material layers that is integrated with a light emitting diode (LED) 15,in which the photovoltaic device 10 is positioned between the supportingsubstrate 5 and the LED 15. The high voltage photovoltaic device 10includes an n-type gallium nitride containing photovoltaic junctionlayer 9, and a p-type gallium nitride containing photovoltaic junctionlayer 8. The n-type gallium nitride containing photovoltaic junctionlayer 9, and a p-type gallium nitride containing photovoltaic junctionlayer 8 that are depicted in FIG. 2 are similar to the n-type galliumnitride containing photovoltaic junction layer 9, and the p-type galliumnitride containing photovoltaic junction layer 8 that are depicted inFIG. 1. Therefore, the above description of the n-type gallium nitridecontaining photovoltaic junction layer 9, and the p-type gallium nitridecontaining photovoltaic junction layer 8 that are depicted in FIG. 1 issuitable for describing the n-type gallium nitride containingphotovoltaic junction layer 9, and a p-type gallium nitride containingphotovoltaic junction layer 8 that are depicted in FIG. 2.

In the embodiment that is depicted in FIG. 2, the photovoltaic device 10is present atop the supporting substrate, and the LED 15 is present atopthe photovoltaic device 10, wherein the LED 15 is at the end of thematerial stack 50 that is the light receiving end of the device. In theembodiment depicted in FIG. 2, the photovoltaic device 10 is presentbetween the supporting substrate 5 and the LED device 15.

The LED device 15 includes a p-type gallium nitride containing layer 12,a quantum well 13 composed of gallium nitride containing layers andindium gallium nitride containing layers, and an n-type gallium nitridecontaining layer 14. The p-type gallium nitride containing layer 12 andthe n-type gallium nitride containing layer 14 may be referred to ascladding layers, and can function to pump charge carriers, i.e.,electron and hole charge carriers, into the intrinsic active areaprovided by the quantum well 13. The p-type gallium nitride containinglayer 12, the quantum well 13, and the n-type gallium nitride containinglayer 14 that are depicted in FIG. 2 are similar to the p-type galliumnitride containing layer 12, the quantum well 13, and the n-type galliumnitride containing layer 14 that are depicted in FIG. 1. Therefore, theabove description of the p-type gallium nitride containing layer 12, thequantum well 13, and the n-type gallium nitride containing layer 14 forthe LED device 15 that is depicted in FIG. 1 is suitable for describingthe p-type gallium nitride containing layer 12, the quantum well 13, andthe n-type gallium nitride containing layer 14 of the LED device 15 thatis depicted in FIG. 2.

Similar to the electrical device 100 a including high voltage GaNphotovoltaic device 10 integrated with an InGaN LED device 15 that isdepicted in FIG. 1, the electrical device 100 b including the highvoltage GaN photovoltaic device 10 integrated with the InGaN includingLED 15 that is depicted in FIG. 2 includes a photovoltaic device 10 thatproduces power greater than 2.0 V, e.g., 2.5 V or greater power, that issuitable for powering the LED 15. The photovoltaic device 10 may producethe aforementioned levels of power by being subjected to a light source3 on the order of 300 nm. In response to the voltage, i.e., power,produced by the photovoltaic device 10, the electrically connected LED15 can emit light having a wavelength on the order of 400 nm or greater,e.g., on the order of approximately 450 nm.

The electrical device 100 b depicted in FIG. 2 also includes asupporting substrate 5, a glass substrate 4, and contacts 21, 22, 31,32. These structures have been described above by the description of thestructures having same reference numbers that are depicted in FIG. 1.

FIG. 3 depicts one embodiment of a high voltage photovoltaic device 10 aincluding material layers of aluminum gallium nitride (AlGaN) that isintegrated with a light emitting diode (LED) device 15 a, in which theLED device 15 a is positioned between the supporting substrate 5 and thephotovoltaic device 10. The LED device 15 a may be present at a firstend of the material stack 50 a having a first set of bandgap materials12 a, 13 a, 14 a; and the photovoltaic device at a second end of thematerial stack having a second set of bandgap materials 8 a, 9 a. Insome embodiments, because the LED device 15 a and the photovoltaicdevice 10 a are included within the same material stack 50 a, thedevices 10 a, 15 a are monolithographically integrated onto the samesupporting substrate 5. In some embodiments, the LED device 15 a and thephotovoltaic device 10 a that are depicted in FIG. 3 are in directcontact, i.e., there is no material layer present between and separatingthe LED device 15 a from the photovoltaic device 10 a. In each of thecombinations of electrical devices described herein, the material layersfor the photovoltaic device 10 a are selected to produce enough power tocause the LED 15 a to emit light. In the embodiments, in which thephotovoltaic device 10 a is present atop the LED 15 a, and the LED 15 aemits light in the direction through the photovoltaic device 10 a, thebandgap materials of the photovoltaic device 10 a and the LED 15 a areselected so that the wavelengths of light emitted by the LED 15 a arenot absorbed by the photovoltaic device 10 a.

In each of the electrical devices described herein, in which thephotovoltaic device 10 a and the LED device 15 a are integrated withinthe same material stack 50 a of semiconductor materials, the bandgaps ofthe materials are selected so that the device having the wider bandgapmaterials, e.g., LED 15 a or photovoltaic device 10 a, is present at thetop of the device, i.e., the light receiving end of the device; and thatthe device having the narrower bandgap materials, e.g., LED 15 a or thephotovoltaic device 10 a, is present at the base of the device, i.e.,the end of the device that is furthest from the light source.

In the embodiment depicted in FIG. 3, the photovoltaic device 10 a ispresent at the end of the material stack 50 a that is closest to thelight source 3 and is composed of a p-type conductivity aluminum,gallium and nitride containing layer 8 a, i.e., p-type aluminum galliumnitride (AlGaN), that forms a junction by direct contact to an n-typeconductivity aluminum, gallium and nitride containing layer 9 a, i.e.,n-type aluminum gallium nitride (AlGaN). The band gap for aluminumgallium nitride (AlGaN) is on the order of 4 eV. The photovoltaic device10 a that is depicted in FIG. 3 when receiving a light wavelengthranging from 200 nm to 300 nm can provide a voltage that is greater than2.5 V. In yet other examples, the voltage provided is greater than 3.0V. For example, the photovoltaic device 10 a that is depicted in FIG. 3that is composed of a junction of n-type and p-type aluminum galliumnitride (AlGaN) layers may provide a voltage of 3.5 V or greater. It isnoted that the prior examples are provided for illustrative purposesonly, and are not intended to limit the present disclosure. In otherexamples, the voltage provided by a photovoltaic device 10 a composed ofa junction of n-type and p-type conductivity aluminum gallium nitride(AlGaN), as depicted in FIG. 3, may be equal to 2.5 V, 2.75 V, 3.0 V,3.25 V and 3.5V, as well as any value between the aforementionedexamples, and any range of voltages having a lower limit provided by oneof the aforementioned examples, and an upper limit provided by one ofthe aforementioned examples.

Each of the p-type conductivity aluminum, gallium and nitrogencontaining layer 8 a, i.e., p-type aluminum, gallium nitride (AlGaN),and the n-type conductivity aluminum, gallium and nitrogen containinglayer 9 a, i.e., n-type aluminum gallium nitride (AlGaN) may have athickness ranging from 100 nm to 2000 nm. The dopant that provides thep-type conductivity of the n-type conductivity aluminum, gallium andnitride containing layer 8 a may be present in a concentration rangingfrom 10¹⁷ atoms/cm³ to 10²⁰ atoms/cm³. The dopant that provides then-type conductivity of the n-type conductivity aluminum, gallium andnitride containing layer 9 a may be present in a concentration rangingfrom 10¹⁷ atoms/cm³ to 10²⁰ atoms/cm³.

In some embodiments, the light to power the photovoltaic device 10 a ofthe p-type conductivity aluminum, gallium and nitride containing layer 8a and the n-type conductivity aluminum, gallium and nitride containinglayer 9 a may range from 200 nm to 325 nm. For example, the light topower the photovoltaic device 10 a having the junction of p-type AlGaNand n-type AlGaN is equal to approximately 250 nm.

The p-type conductivity aluminum, gallium and nitride containing layer 8a and the n-type conductivity aluminum, gallium and nitride containinglayer 9 a of the photovoltaic device 10 a provide a first set of bandgapmaterials, while the material layers in the LED 15 a provide a secondset of bandgap materials. The minimum bandgap for the first set ofbandgap materials, i.e., the minimum bandgap materials for the materiallayers in the photovoltaic device 10 a, is wider than the minimumbandgap for the second set of bandgap materials, i.e., the minimumbandgap materials for the material layers in the LED 15 a.

Referring to FIG. 3, the second end of the material stack 50 a includesthe light emitting diode (LED) 15 a. In the embodiment that is depictedin FIG. 3, the LED 15 a is positioned between the supporting substrate 5and the photovoltaic device 10 a, wherein the supporting substrate 5 iscomprised of n-type aluminum gallium nitride (n-type AlGaN). The n-typealuminum gallium nitride containing photovoltaic junction layer 9 a isin direct contact with the LED device 15 a. The LED device 15 a mayinclude a p-type aluminum gallium nitride containing layer 12 a that isin direct contact with a first end of a multi quantum well 13 a, and ann-type aluminum gallium nitride containing layer 14 a that is directcontact with an opposing second end of the multi quantum well 13 a. Thep-type aluminum gallium nitride containing layer 12 a of the LED 15 amay be referred to as a first cladding layer, and the n-type galliumnitride containing layer 14 a may be referred to as a second claddinglayer.

In some embodiments, the first and second cladding layers, i.e., thep-type aluminum gallium nitride containing layer 12 a and the n-typealuminum gallium nitride containing layer 14 a, function to pump chargecarriers, i.e., electron and hole charge carriers, into the intrinsicactive area provided by the quantum well 13 a. The dopant that providesthe conductivity type, i.e., whether the aluminum gallium nitridecontaining layer 12 a, 14 a is n-type or p-type, may be present in aconcentration ranging from 10¹⁷ atoms/cm³ to 10²⁰ atoms/cm³. In someexamples, the p-type aluminum gallium nitride containing layer 12 a andthe n-type aluminum gallium nitride containing layer 14 a may have athickness ranging from 100 nm to 2000 nm. It is noted that the abovecompositions and thicknesses are provided for illustrative purposesonly, and are not intended to limit the present disclosure.

The active region of the LED 15 a is in the intrinsic (I) region, whichis present in the quantum well 13 a. The active region in the quantumwell structure is formed by alternating layers of relatively low bandgapmaterial and layers of relatively high bandgap material. As used herein,a “low bandgap” is a bandgap ranges from 0.5 eV to 3.75 eV, and a “highbandgap” ranges from 3.8 eV to 4.5 eV. The former layers are termed“well layers” and the latter layers are termed “barrier layers.” Forexample, for the quantum well 13 a, e.g., multi-quantum well, thematerial layers providing the relatively high bandgap material may bealuminum gallium nitride (AlGaN) having a bandgap of approximately 4 eV,and the material layers having the relatively low bandgap material maybe gallium nitride (GaN) having a bandgap of approximately 3.4 eV. Theband gap of approximately 3.4 eV for the gallium nitride (GaN) portionof the multi-quantum well provides that the minimum value for the secondset of bandgap materials for the material layers in the LED 15 a is lessthan the minimum value, i.e., is narrower, than the minimum bandgap ofthe wider bandgap materials for the overlying first set of bandgapmaterials for the material layers in the photovoltaic device 10 providedby aluminum gallium nitride (AlGaN) having a band gap of 4.0 eV.

To provide the stacked structure of quantum wells, the thickness of eachlayer of semiconductor material within the quantum well may be nogreater than 50 nm. For example, the thickness for each layer of theIII-V compound semiconductor material, e.g., high band gap AlGaN and/orlow band gap GaN, within the quantum well 13 a may range from 5 nm to 10nm. In some embodiments, the stacked structure of quantum wells may becomposed of 1 to 100 layers of semiconductor material, such as III-Vcompound semiconductor materials, e.g., the high band gap AlGaN and/orlow band gap GaN. In yet another embodiment, the stacked structure ofquantum wells may be composed of 1 to 5 layers of semiconductor materiallayers.

The active region consisting of one or more gallium nitride (GaN) andaluminum gallium nitride (AlGaN) including quantum wells 13 a sandwichedbetween thicker layers of n-type and p-type doped aluminum galliumnitride (AlGaN) layers 12 a, 14 a, i.e., cladding layers 12 a, 14 a, mayprovide an LED 15 a that provides for ultra violet (UV) light emission,i.e., light emission at wavelengths of 400 nm or less. For example, theLED device 15 a that is depicted in FIG. 3 may emit light having awavelength of approximately 350 nm. The wavelength of light beingemitted by the LED device 15 a is not absorbed by the photovoltaicdevice 10 a that the light from the LED device 15 a is being passedthrough. It is noted that the wavelength of approximately 350 nm is onlyone example of a light wavelength that may be emitted by the LED device15 a. In some other examples, the light wavelength that may be emittedby an LED device 15 a similar to that depicted in FIG. 3 may be equal to300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm, 360 nm, 370 nm, 380 nm,390 nm and 400 nm, as well as any range of values having a lower limitselected from the aforementioned examples, and an upper limit selectedfrom the aforementioned examples, e.g., a range extending from 330 nm to370 nm. As noted above, the LED device 15 a may be powered by thevoltage produced by the photovoltaic device 10 a, e.g., a voltage ofgreater than 2.5 V. In some embodiments, the LED device 15 a may bepowered by the voltage produced by the photovoltaic device 10 a, e.g., avoltage greater than 3.0 V.

The LED device 15 a may be positioned on semiconductor substrate 5. Insome embodiments, the semiconductor substrate 5 is composed of an n-typeIII-V semiconductor material, such as aluminum gallium nitride, e.g.,n-type AlGaN.

The high voltage GaN photovoltaic cells that are integrated with InGaNLED structures that are depicted in FIG. 3 may also include a glasssubstrate 4 on the light 3 receiving end of the device.

The electrical device 100 c depicted in FIG. 3 also includes contacts21, 22, 31, 32. These structures have been described above by thedescription of the structures having same reference numbers that aredepicted in FIG. 1.

FIG. 4 depicts another embodiment of an electrical device 100 dincluding a high voltage photovoltaic device 10 b of gallium nitride(GaN) material layers that is integrated with a light emitting diode(LED) 15, in which the photovoltaic device 10 b is positioned betweenthe supporting substrate 5 and the LED 15 b. The high voltagephotovoltaic device 10 b includes an n-type gallium nitride containingphotovoltaic junction layer 9 b, and a p-type gallium nitride containingphotovoltaic junction layer 8 b. The n-type gallium nitride containingphotovoltaic junction layer 9 b, and a p-type gallium nitride containingphotovoltaic junction layer 8 b that are depicted in FIG. 4 are similarto the type gallium nitride containing photovoltaic junction layer 9,and a p-type gallium nitride containing photovoltaic junction layer 8that are depicted in FIG. 1. Therefore, the above description of then-type gallium nitride containing photovoltaic junction layer 9, and thep-type gallium nitride containing photovoltaic junction layer 8 that aredepicted in FIG. 1 is suitable for describing the n-type gallium nitridecontaining photovoltaic junction layer 9 b, and a p-type gallium nitridecontaining photovoltaic junction layer 8 b that are depicted in FIG. 4.

In the embodiment that is depicted in FIG. 4, the LED 15 b is presentatop the supporting substrate 5, and the photovoltaic device 10 b ispresent atop the LED 15 b, wherein the LED 15 b is at the end of thematerial stack 50 that is the light receiving end of the device. In theembodiment depicted in FIG. 4, the LED 15 b is present between thesupporting substrate 5 and the photovoltaic device 10 b.

The LED 15 b includes a p-type aluminum gallium nitride containing layer12 b, a quantum well 13 b composed of aluminum gallium nitridecontaining layers and indium gallium nitride containing layers, and an-type aluminum gallium nitride containing layer 14 b.

The p-type aluminum gallium nitride containing layer 12 b and the n-typealuminum gallium nitride containing layer 14 b may be referred to ascladding layers, and can function to pump charge carriers, i.e.,electron and hole charge carriers, into the intrinsic active areaprovided by the quantum well 13 b. The p-type aluminum gallium nitridecontaining layer 12 and the n-type aluminum gallium nitride containinglayer 14 that are depicted in FIG. 4 are similar to the p-type aluminumgallium nitride containing layer 12 a, and the n-type aluminum galliumnitride containing layer 14 a that are depicted in FIG. 3. Therefore,the above description of the p-type aluminum gallium nitride containinglayer 12 a and the n-type aluminum gallium nitride containing layer 14 afor the LED device 15 a that is depicted in FIG. 3 is suitable fordescribing the p-type aluminum gallium nitride containing layer 12 b andthe n-type aluminum gallium nitride containing layer 14 b of the LEDdevice 15 b that is depicted in FIG. 4.

The active region of the LED device 15 b is in the intrinsic (I) region,which is within the quantum well 13 b. The active region in the quantumwell structure is formed by alternating layers of relatively low bandgapmaterial and layers of relatively high bandgap material. As used herein,a “low bandgap” is a bandgap ranges from 0.5 eV to 3.4 eV, and a “highbandgap” ranges from 3.5 eV to 4.5 eV. The former layers are termed“well layers” and the latter layers are termed “barrier layers.” Forexample, for the quantum well 13 b, e.g., multi-quantum well, thematerial layers providing the relatively high bandgap material may bealuminum gallium nitride (AlGaN), and the material layers having therelatively low bandgap material may be indium gallium nitride (InGaN).Indium gallium nitride (InGaN) has a band gap of approximately 2.7 eV,while aluminum gallium nitride (GaN) has a band gap of approximately 4.0eV.

To provide the stacked structure of quantum wells, the thickness of eachlayer of semiconductor material within the quantum well may be nogreater than 50 nm. In some embodiments, the stacked structure ofquantum wells may be composed of 1 to 100 layers of semiconductormaterial. In yet another embodiment, the stacked structure of quantumwells 13 b may be composed of 1 to 5 layers of semiconductor materiallayers.

The electrical device 100 d depicted in FIG. 4 also includes asupporting substrate 5, a glass substrate 4, and contacts 21, 22, 31,32. These structures have been described above by the description of thestructures having same reference numbers that are depicted in FIG. 1.

The structures depicted in FIGS. 1-4 are now described with more detailin the following description of methods for forming high voltagephotovoltaic cells that are integrated with LEDs.

FIG. 5 is a flow chart illustrating one embodiment of a method forforming high voltage photovoltaics that are integrated with LEDs, suchas those depicted in FIGS. 1 and 3, in which the method includes a lowhydrogen deposition process. The term “low hydrogen” denotes that thedeposition step has a maximum hydrogen content of 1×10¹⁸ cm⁻³.

The method may begin at step 101 with forming lower junction by metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy(MBE). The lower junction may be formed on a supporting substrate 5,such as an n-type gallium nitride (GaN) substrate, as depicted in FIGS.1 and 3. The lower junction that is formed may provide an LED 15, 15 a,as depicted in FIGS. 1 and 3. For example, the lower junction mayprovide an LED 15 depicted in FIG. 1 is composed of a p-type galliumnitride layer 12, as a first cladding layer of the LED 15; a quantumwell of including gallium nitride and indium gallium nitride layers; andan n-type gallium nitride layer 14, as a second cladding layer of theLED 15. For example, the lower junction may provide an LED 15 a depictedin FIG. 3 is composed of a p-type aluminum gallium nitride layer 12 a,as a first cladding layer of the LED 15 a; a quantum well 13 a includinggallium nitride and aluminum gallium nitride layers; and an n-typealuminum gallium nitride layer 14 a, as a second cladding layer of theLED 15 a.

The material layers of the lower junction may be formed using epitaxialgrowth. The terms “epitaxial growth and/or deposition” means the growthof a semiconductor material on a deposition surface of a semiconductormaterial, in which the semiconductor material being grown hassubstantially the same crystalline characteristics as the semiconductormaterial of the deposition surface. The term “epitaxial material”denotes a material that is formed using epitaxial growth. In someembodiments, when the chemical reactants are controlled and the systemparameters set correctly, the depositing atoms arrive at the depositionsurface with sufficient energy to move around on the surface and orientthemselves to the crystal arrangement of the atoms of the depositionsurface. Thus, in some examples, an epitaxial film deposited on a {100}crystal surface will take on a {100} orientation.

The epitaxial growth process may be by chemical vapor deposition (CVD)or molecular beam epitaxy (MBE) growth processes.

MBE growth processes can include heat the substrate, which can be tosome hundreds of degrees (for example, 500-600° C.) in the case ofgallium nitride). In a following step, MBE growth processes include aprecise beam of atoms or molecules (heated up so they're in gas form)being fired at the substrate from “guns” called effusion cells. Thecomposition of the molecules being fired in the beams provide thecomposition of the deposited material layer. The molecules land on thesurface of the substrate, condense, and build up systematically inultra-thin layers, so that the material layer being grown forms oneatomic layer at a time.

Chemical vapor deposition (CVD) is a deposition process in which adeposited species is formed as a result of chemical reaction betweengaseous reactants at greater than room temperature (25° C. to 900° C.);wherein solid product of the reaction is deposited on the surface onwhich a film, coating, or layer of the solid product is to be formed.Variations of CVD processes include, but not limited to, AtmosphericPressure CVD (APCVD), Low Pressure CVD (LPCVD) and Plasma Enhanced CVD(PECVD), Metal-Organic CVD (MOCVD) and combinations thereof may also beemployed. In some preferred embodiments, the CVD process used to formthe lower junction may be metal organic chemical vapor deposition.

A number of different sources may be used for the deposition ofepitaxial type III-V semiconductor material. In some embodiments, thesources for epitaxial growth of type III-V semiconductor materialinclude solid sources containing In, Ga, N, P elements and combinationsthereof and/or a gas precursor selected from the group consisting oftrimethylgallium (TMG), trimethylindium (TMI), Trimethylaluminum (TMA),tertiary-butylphosphine (TBP), phosphine (PH₃), ammonia (NH₃), andcombinations thereof. The temperature for epitaxial deposition of typeIII-V semiconductor materials may range from 550° C. to 900° C. Althoughhigher temperature results in faster deposition, the faster depositionmay result in crystal defects and film cracking.

The material layers for the lower junction may be doped n-type or p-typeusing in situ doping. By “in-situ” it is meant that the dopant thatprovides the conductivity type of the material layer, e.g., materiallayer that contributes to providing a junction, is introduced as thematerial layer is being formed. To provide for in-situ doped p-type orn-type conductivity, the dopant gas may be selected from the groupconsisting of bis-cyclopentadienyl-magnesium (Cp₂Mg), silane (SiH₄),disilane (Si₂H₆), germane (GeH₄), carbon tetrabromide (CBr₄) andcombinations thereof. The intrinsic materials of the quantum wells 13,13 a are not doped with n-type or p-type dopant.

In a following step 102, the dopants within the first junction areactivated. Activation anneal may be conducted at a temperature rangingfrom 850° C. to 1350° C. Activation annealing may be provided by furnaceannealing, rapid thermal annealing (RTA) or laser annealing.

At step 103, the method continues by forming the upper junction using alow hydrogen deposition process, such as MBE growth methods. In theexamples illustrated in FIGS. 1 and 3, the upper junction is aphotovoltaic device 10, 10 a that is epitaxially formed directly on LED15, 15 a. In the embodiment depicted in FIG. 1, the photovoltaic device10 may include a p-type gallium nitride (p-type GaN) layer 8 and ann-type gallium nitride (n-type GaN) layer 9. In the embodiment depictedin FIG. 3, the photovoltaic device 10 a may include a p-type aluminumgallium nitride (p-type AlGaN) layer 8 a and an n-type aluminum galliumnitride (n-type AlGaN) layer 9 a.

It has been determined that hydrogen precursors can deactivate theelectrically activated p-type dopant in the underlying p-type galliumnitride containing layers and/or p-type aluminum gallium containingnitride layers of the underlying LEDs 15, 15 a. Therefore, the methodfor depositing the material layers of the photovoltaic devices 10 a, 10b can employ a low-hydrogen containing process, e.g., deposition methodusing hydrogen free precursors, such as MBE. A second activation annealmay be formed after the formation of the upper junction. The activationanneal may be conducted at a temperature ranging from 850° C. to 1350°C. Activation annealing may be provided by furnace annealing, rapidthermal annealing (RTA) or laser annealing.

At step 104, the upper and lower junction may be patterned and etched toprovide the geometry for each photovoltaic device 10, 10 a, 10 b, andeach LED 15, 15 a, 15 b. The upper and lower junctions may be patternedusing photolithography and etch processes. For example, a photoresistmask may be formed on the uppermost semiconductor layer by applying aphotoresist layer, exposing the photoresist layer to a pattern ofradiation, and then developing the pattern into the photoresist layerutilizing conventional resist developer. In some embodiments, the blockmasks have a thickness ranging from 100 nm to 300 nm. The exposedportions of the semiconductor material layers that provide the upper andlower junctions may then be etched using an etch process, such as ananisotropic etch, e.g., reactive ion etch (RIE), or an isotropic etch,such as a wet chemical etch. In some embodiments, a first pattern andetch sequence including a first etch mask may be used to define thegeometry of the upper junction; and a second pattern and etch sequenceincluding a second etch mask may be used to define the geometry of thelower junction.

Thereafter, the contacts 21, 22, 31, 32 may be formed to each of theupper and lower junctions, i.e., photovoltaic device 10, 10 a, 10 b andthe LED 15, 15 a, 15 b, using deposition, photolithography and etchingprocesses. For example, a metal layer can be deposited using a physicalvapor deposition (PVD) process. The PVD process may include plating,electroplating, electroless plating and combinations thereof. Thedeposited metal layers may be patterned and etched using deposition,photolithography and etching to provide the desired geometry of thecontacts 21, 22, 31, 32.

FIG. 6 is a flow chart of another embodiment of a method for forminghigh voltage photovoltaics that are integrated with LEDs. The processflow depicted in FIG. 6 does not require a low hydrogen forming method.At steps 201 and 202 the lower and upper junctions may be epitaxiallyformed. In some embodiments, the lower and upper junctions may be formedusing the chemical vapor deposition, e.g., MOCVD, and MBE formingmethods that have been described above with reference to FIG. 5 forsteps 101 and 103.

At step 203, at least the upper junction of the device is patterned toprovide the geometry of the desired photovoltaic device 10, 10 a, 10 band/or the LED 15, 15 a, 15 b. The pattern step described in step 203 issimilar to the patterning step described at step 104 of the process flowdescribe with reference to FIG. 5. Therefore, the above describedphotolithography and etch steps described with reference to step 104 ofFIG. 5 are applicable to an least one example of the patterning step forstep 203 of the process flow illustrated in FIG. 6.

At step 204, the n-type and p-type dopants for the material layer of theupper and lower junction are activated by an activation anneal. Theactivation anneal at step 204 of the process flow for the method in FIG.6 is similar to the activation anneal at step 102 of the methodillustrated in FIG. 5. Therefore, the above description of theactivation anneal for step 102 for the method illustrated in FIG. 5 issuitable for describing one embodiment of the activation anneal that canbe used at step 204 of the method depicted in FIG. 6.

At step 205, contacts 21, 22, 31, 32 are formed to the upper and lowerjunctions of the device.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

The invention claimed is:
 1. An electrical device comprising: a materialstack present on a supporting substrate; an LED device at a first end ofthe material stack having a first set of bandgap materials; and aphotovoltaic device at a second end of the material stack having asecond set of bandgap materials, the second end of the material stackbeing a light receiving end, wherein a widest bandgap material for thesecond set of bandgap material is greater than a highest bandgapmaterial for the first set of bandgap materials; wherein the LED deviceis disposed directly between the supporting substrate and thephotovoltaic device.
 2. The electrical device of claim 1, wherein thesupporting substrate is comprised of n-type gallium nitride.
 3. Theelectrical device of claim 2, wherein the photovoltaic device comprisesa p-type gallium nitride containing photovoltaic junction layer indirect contact with an n-type gallium nitride containing photovoltaicjunction layer.
 4. The electrical device of claim 3, wherein the n-typegallium nitride containing photovoltaic junction layer is in directcontact with the LED device, the LED device including a p-type galliumnitride containing layer that is in direct contact with a first end of amulti quantum well and an n-type gallium nitride containing layer thatis direct contact with an opposing second end of the multi quantum well.5. The electrical device of claim 2, wherein the photovoltaic devicecomprises a p-type aluminum gallium nitride containing photovoltaicjunction layer in direct contact with an n-type aluminum gallium nitridecontaining photovoltaic junction layer.
 6. The electrical device ofclaim 5, wherein the n-type aluminum gallium nitride containingphotovoltaic junction layer is in direct contact with the LED device,the LED device including a p-type gallium nitride containing layer thatis in direct contact with a first end of a multi quantum well and ann-type gallium nitride containing layer that is direct contact with anopposing second end of the multi quantum well.
 7. An electrical devicecomprising: a material stack present on a supporting substrate; an LEDdevice at a first end of the material stack, the LED device having afirst set of bandgap materials; and a photovoltaic device at a secondend of the material stack having a second set of bandgap materials, thefirst end of the material stack being a light receiving end, wherein awidest bandgap material for the first set of bandgap material is greaterthan a widest bandgap material for the second set of bandgap materials;wherein the photovoltaic device comprises a p-type gallium nitridecontaining photovoltaic junction layer in direct contact with an n-typegallium nitride containing photovoltaic junction layer; and wherein theLED device is disposed directly between the supporting substrate and thephotovoltaic device.
 8. The electrical device of claim 7, wherein thesupporting substrate is comprised of n-type gallium nitride.
 9. Theelectrical device of claim 8, wherein the p-type gallium nitridecontaining photovoltaic junction layer is in direct contact with the LEDdevice, the LED device including a p-type aluminum gallium nitridecontaining layer that is in direct contact with a first end of a multiquantum well and an n-type aluminum gallium nitride containing layerthat is direct contact with an opposing second end of the multi quantumwell, the n-type aluminum gallium nitride containing layer being indirect contact with the photovoltaic device.